Once in a blue dune…On the floor of the Lyot Crater on Mars lies a field of dunes. One particular dune, seen in this January view, appears turquoise blue in enhanced color & is made of a different composition than the surrounding dune field. Take a look: https://t.co/zeVqWJHO1ipic.twitter.com/PlMNFI4VQr

The reason for the enhanced coloring is because the MRO's camera, the High Resolution Imaging Science Experiment or HiRISE, can take photographs at wavelengths broader than what the human eye can see naturally, and often takes photos in infrared. Since there's no way to easily translate infrared colors into anything we humans are capable of seeing, enhancing the image is often necessary.